REMPI and MATI spectroscopy of cis and trans 3-chloro-N-methylaniline

Abstract

The Resonance-enhanced two-photon ionization (R2PI) and Mass-analyzed threshold ionization (MATI) spectra of 3-Chloro-N-methylaniline (3ClNMA) were recorded in detail. The experimental and calculated results revealed that cis and trans 3ClNMA are the only two stable conformers for each of the S0, S1 and D0 states. The first electronic excitation energies (E1s) of cis and trans35Cl-3ClNMA were measured to be 33,003±3 and 32,886±3cm−1 by R2PI spectroscopy. The adiabatic ionization energies (IEs) of cis and trans35Cl-3ClNMA were determined to be 61,531±5 and 61,625±5cm−1 by MATI spectroscopy. The E1s and IEs of cis and trans37Cl-3ClNMA were also obtained and found to be identical to that of the 35Cl-3ClNMA rotamers. Compared with the trans rotamer, the cis rotamer is less stable by 50cm−1 in the S1 state, but more stable by 67 and 161cm−1 in S0 and D0 states. Most of the active vibration modes observed in the R2PI and MATI spectra are in-plane ring deformation and substituent-sensitive modes. Detailed analysis reveals a correlation between the typical ring vibration frequencies and the relative stability of the two rotamers, suggesting that the conformation effect on the ring rigidity plays a key role in determining the relative stability of the conformers. The ab initio and density functional theory (DFT) calculations were performed to analyze the substitution and conformation effects on the properties of 3ClNMA rotamers.